Glow plugs for compression ignition engines



.M y'5, 1959 G. HNMOULE ET AL 2,

GLOW PLUGS FOR COMPRESSION IGNITION ENGINES Filed Oct. 25, 1955 2 Sheets-Sheet 1 FIQ.4:-

' INVENTORS M M il [A [9cm ATTORNEYS y 1959 G. H. MOULE E 2,884,920

GLOW PLUGS FOR COMPRESSION IGNITION ENGINES Filed 001;. 25, 1 955 2 Sheets-Sheet 2 ATTORNEYS INVENTORS 2' 4 M 9% M United States Patent GLOW PLUGS FOR COMPRESSION IGNITION ENGINES Gordon Henry Moule, Old Tratford, Manchester, and

John Thomas Urry, Sale, England, assignors to Metropolitan-Vickers Electrical Company Limited, a British company Application October 25, 1955, Serial No. 542,604

Claims priority, application Great Britain October 29, 1954 2 Claims. (Cl. 123-145) This invention relates to electrical glow plugs and in particular to glow plugs for use in starting compression ignition engines. A glow plug is essentially an electric heating element device whose function is to provide a hot spot, preferably between 900 to 1,000 deg. cent., in the cylinder combustion or pre-combustion chamber to assist in igniting the fuel gases when the engine is started up from cold. In particularly low temperatures, an additional heat source of this type is essential before firing in the cylinder will occur at all, but once regular firing is achieved, and the mass of the engine generally warmed up, the engine will continue to run without the aid of the plugs which can then be switched off.

In practice, the plugs are first energised for initial starting, and usually kept on for approximately 2 minutes to ensure regular firing and then cut out. The plugs will not be used again until the engine has been left inoperative long enough to reach the cold-start condition again.

The heating element of each glow plug is usually located in a recess in the engine cylinder head connecting up with the combustion or pre-combustion chamber for each cylinder, and the tip or hot spot of the element is usually made to line up with the wall of the combustion chamber or an auxiliary chamber, e.g. a pre-combustion chamber. The heating element, whether energised or not, is thus always in contact with the hot combustion gases as long as the engine is running, and it is essential, therefore, that it should be of robust construction to withstand the pressure and temperature condition obtaining. The element should also be capable of reaching its peak temperature in a short period of time, usually less than 45 seconds, to achieve reasonable starting times, and further, the current consumption should be as low as possible since, with a number of plugs per engine, this can represent a very heavy current drain on the battery during the time the plugs are energised.

In the application of glow plugs for the small size diesel engines now being developed for motor car use, the factors of physical size and low current consumption are of prime importance, as glow plugs usually have to be located between other components such as valves and valve operating gear.

According to the present invention a glow plug for starting a compression ignition engine comprises a cylindrical plug body adaptedfor insertion and screw threaded location in a port in walling of a combustion or associated chamber of an engine, a tubular sheathed heating element extending axially from the inner end thereof, i.e. the end adapted for insertion, and an electrical terminal at the outer end of the plug body, the heating element comprising a heater coil substantially contained within that part of said heating element which protrudes from the inner end of the plug body, one end of the heater coil being electrically connected to the protruding end of the sheath and the other being electrically conice nected through a lead or extension lead with said terminal.

The invention also comprises a compression ignition engine having means for starting, consisting of a glow plug (or plugs) as specified in the preceding paragraph, located and secured by means of a screw thread joint within a port (or ports) of a combustion or associated chamber (or chambers) of said engine and so arranged that the hot end of the heating element (or elements) is in contact with the gases in said chamber.

In carrying out the invention there will be a glow plug for each cylinder, thus a single cylinder engine will only have a single glow plug but a multi cylinder engine will have a corresponding number of glow plugs. The glow plugs may be in contact with the combustible gases and fuel in the actual combustion chamber or an associated chamber such as an air swirl chamber or pre-combustion chamber.

In arrangements embodying the invention the hot end of the heater element may either project into the chamber of the engine or it may be bent around so as to present a hot surface which is in alignment with the surface of the wall bounding the chamber.

In order that the invention may be more clearly understood reference will now be made to the accompanying drawings, in which:

Fig. l is a section of one form of heating element.

Fig. 2 is a view of an assembled glow plug in which the hot end of the heater has been bent into an incomplete annulus.

Fig. 3 is an end view of the glow plug shown in Fig. 2.

Fig. 4 is a section of a combustion chamber of a compression ignition engine showing a glow plug of the kind shown in Figs. 1 and 2 in position.

Fig. 5 shows an alternative arrangement of glow plug in which the heater element is not bent.

In the arrangement shown in Figs. l-4 the heating element consists of a tubular metal sheath 1 which is lined with magnesium oxide 2, deposited by a suitable magnesium conversion process. The end of the sheath which protrudes from the inner end of the plug body contains a helical heating coil 3. This end of the sheath is tapered to form a small hole through which one tail end 4 of the heating coil protrudes, where it is fused or welded to the sheath to form an electrical connection thereto 5, the fusion or welding being such as to provide a pressure-tight seal to the end of the sheath. The other longer tail 6 of the heating coil is strengthened by a fine metal tube 7 slipped over its end, which extends axially beyond the open end of the tubular sheath and is insulated from the tubular metal sheath by the inner lining of magnesium oxide 2. The whole of the inner space of the tubular metal sheath is packed with sand. The tubular metal sheath is extended axially beyond its open end by attaching thereto a further short length of metal tubing 8 of the same diameter. The two tubes are slid over the opposite ends of a short length of ceramic tubing 9 whose outer diameter is the same as the inner diameters of the metal tubes, thus providing a means of aligning the metal tubes one with the other. The ends of the metal tubes are separated by an annular spacer of glass 10 which secures the two metal tubes to the ceramic tube 9, provides a pressure-tight seal and ensures that the two metal tubes are electrically insulated from one another. The attached short length of metal tubing 8 is packed with stranded wire 11 around the axially placed thin metal tube 7 which supports the heating coil tail wire 6, crimped at a point 13' about half-way along its length in order to provide an electrical connection to said tail wire by Way of the stranded wire packing, and closed at its open end by a screwed terminal 12 which is buttwelded thereto. Thus an electrical connection is provided from the heating coil 3 by way of the tail wire 6, its

supporting metal tube 7, the stranded wire packing 11 and the crimped metal tube to the screwed terminal 12. The heating element is located in and extends axially through the plug body (Fig. 2). The sealed end of the heating element projects a short way from the inner end 14 of the plug body and this projecting portion is bent into the form of an incomplete annular ring 15 of diameter about that of the plug body. At the point of entry into the plug body the tubular metal sheath of the heating element is welded 16 to the end of the plug body to provide mechanical securing and an electrical connection between the heating coil, the plug body and the frame of the engine in which the plug is secured. The screwed terminal 12 projects from the outer end of the plug body 13. The plug body itself is a solid cylindrical metal part, axially bored to take the heating element, and provided with a threaded portion 17 for location in the body of an engine and with a part of the cylinder outer wall machined to provide a hexagonal head 18 for effecting mechanical engagement with a spanner. The outer end 19 (Fig. 4) of the bore of the plug body is counter-bored and sleeved with an electrical insulator 253 so that the screw terminal and attached metal tube 8 are electrically insulated from the plug body, but the tubular metal sheath 1 is not so insulated. The screwed terminal 12 is further insulated from the plug body by the mica washer 27 and the annular glass seal 28, the lug of the supply cable to the plug being secured by the nut 29.

In use the glow plug fits into'an engine port 21 of a combustion chamber 22 of a compression ignition engine. The part of the heater element which projects from the plug body and comprises the incomplete annulus is of such dimensions that, when the glow plug is secured in place, the face 23 of the annulus 15 is in line with the face 24 of the combustion chamber wall. The diameter of the annulus is almost the same as that of the port. The glow plug is seated in a gland 25, fixed in the cylinder head 26 of the engine.

In the arrangement shown in Fig. 5 the sheath of the heating element 1 is a close fit inside a bore of the plug body 37 which has a hexagon head 38 flanged at 39. The body 37 has a tapered end 35 to provide a conical seat for pressure sealing with the usual copper asbestos washer when the plug is screwed into the cylinder head. The heating element is lined with magnesium oxide 2 tightly packed around the axially positioned heater coil 3 of which one end passes through a small hole in the end of the metal sheath 1 and is flash butt-welded thereto at the point 5 thereby providing electrical contact. The heater coil itself is concentrated within that part of the heating element which protrudes from the plug body so that there is no direct path by which heat may be conducted from the coil through the plug body to the cylinder block. The other end of the heater coil is led through the supporting tube 34 and secured to the screwed terminal 12 by being crimped to an extension of the screwed terminal at 30. The magnesium oxide insulation layer is extended back inside the tubular sheath to the seal 31 which has a high temperature operating thermal setting insulator such as Ethoxyline Resin, and the Whole sealing assembly is fixed by an end cap 33 of any suitable insulating material screwed into an extension '39 of the plug body 37. The bore in the plug body is countersunk at 36 to allow the heating element sheath 1 to be brazed to the plug body to provide the electrical connection from the point 4 to the engine frame and to seal the plug against the combustion gases. The whole plug screws into the cylinder head against a copper asbestos washer 35 and the inner end of the element projects into the pre-combustion chamber 22, as shown in the figure.

It will be appreciated that with such an arrangement, heat losses due to conduction through the plug body are 4 diminished by concentrating the heater coil within the end part of the heating element which extends outside the inner end of the plug body. Moreover, the heater coil itself is protected by the sheath from direct contact with the hot combustion gases. The protecting sheath is preferably of a heat-resisting and corrosion-resisting material.

The diameter of the heating element and of the supporting plug body should be made small so as to permit of their use in engines where space in the cylinder head is very restricted.

Preferably the heater has sufiiciently high resistance to enable it to operate ofi a 12-volt or 24-volt battery supply so that a number of plugs may be operated in parallel, and for the same amount of heat energy supplied a lower current drain results than in the case of low resistance heaters. The arrangement permits a single lead being provided to the central screwed terminal from the battery, the return being through the engine frame.

One material that may be used for the tubular metal sheath for the heating element is an alloy of nickel, chromium, and iron, known under the trademark Inconel, and for the heating coil, wire marketed under the trademark Kanthal A.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A glow plug for starting a compression ignition engine and adapted to be mounted in a port extending through a wall of said engine to an internal chamber comprising a cylindrical plug body, a tubular sheathed electrically conductive heating element carried by and having an end portion extending axially from the inner end of the plug body, an electrical terminal at the outer end of the plug body, an electrical heater coil located within the inner end of the sheathed element, an electrical connection between one end of the heater coil and the inner end of the sheathed element, a connecting lead between the other end of the heater coil and the terminal, insulation means for said connecting lead and heater coil providing a circuit from the terminal through said heater coil to said sheath, said inner end portion of said element being bent about the plug axis to provide an incomplete annulus, and means for mounting said glow plug on the engine in said port so that said annulus is substantially aligned with the chamber surface surrounding said port.

2. In a compression ignition engine, a glow plug hav ing a screw threaded coupling for detachably locating it in a port in a wall of the engine, a tubular sheathed heatin element extending axially from the inner end of the plug body towards a chamber of the engine into which combustible fuel enters and bent about the plug axis into an incomplete annulus located in a transverse plane aligned with the wall of said chamber, an electrical terminal at the outer end of the plug body, an electrical heater coil located at the said inner end of the sheathed element, an electrical connection between one end of the heater coil and the inner end of the sheathed element, a connecting lead between the other end of the heater coil and said terminal, and insulation means for said connecting lead and said heater coil providing a circuit from the terminal through the heater coil to said sheath.

References Cited in the file of this patent UNITED STATES PATENTS 1,237,851 Wygodsky Aug. 21, 1917 2,130,365 Paulson Sept. 20, 1938 2,205,145 Klingner June 18, 1940 2,672,546 Klingner Mar. 16, 1954 FOREIGN PATENTS 472,814 Great Britain Sept. 30, 19.37 

